A tiny bug with a big appetite: UF researchers say scale insect attacks more than 300 species of plants

February 16, 2006

FORT LAUDERDALE, Fla. — Welcome to the bug-of-the-month club. Thanks to Florida’s balmy climate and popularity as a tourist destination, at least one new and unwanted insect pest hitchhikes its way into the state every month, according to University of Florida researchers.

One of the most menacing newcomers is the lobate lac scale (Paratachardina lobata), an insect native to India and Sri Lanka that attacks more than 300 types of woody plants, says Forrest Howard, an associate professor of entomology with UF’s Institute of Food and Agricultural Sciences.

“No bigger than a pinhead, the insect could become the most difficult problem yet for trees and shrubs grown as ornamentals in urban areas and native plants in natural areas in South Florida,” he said. “Lobate lac scale is especially serious because it attacks a wide range of host plants, building up extremely dense populations, weakening and in many cases killing the plant.”

Howard said lobate lac scale, like other scale insects that are spread from one country to another, probably arrived on a living plant. The scales are very tiny and colored to blend with the plant, thereby escaping the eyes of agricultural inspectors at a port of entry.

“In 1999 when we first identified the insect in Broward County, we found it on about 10 different kinds of plants in a small area,” he said. “As it continued to spread across South Florida, we have now identified more than 300 species of woody plants that the lobate lac scale attacks.”

These include native species such as wax-myrtle, cocoplum, red bay, wild-coffee and strangler fig as well as commercial fruit trees such as mango, lychee and star fruit.

“Wax-myrtles are obviously the most susceptible to the scale, and these are important berry-producing trees for birds in South Florida,” he said.

Hong Liu, a plant ecologist who works with Howard at UF’s Fort Lauderdale Research and Education Center, is studying the effects of lobate lac scale on the ecology of natural woodlands.

“The wide range of hosts makes lobate lac scale especially troubling,” Liu said. “Evidence of their sap-sucking destruction includes blackened leaves and branches, branch dieback and even death for susceptible shrubs and trees.”

Worse yet, the lobate lac scale may eventually spread to other areas of Florida. “Our laboratory experiments have shown that the scale insects survive below freezing temperatures, indicating a potential spread of the pest into cooler areas of the state,” Howard said.

Howard and his co-workers recently reported several highly effective insecticide treatments that protect plants from this scale. However, for long-term management of the pest, biological control with natural predators is the most viable option.

In an effort to develop a biological control for this pest, Howard is working with Bob Pemberton, an entomologist at the USDA Agricultural Research Service’s Invasive Plant Research Facility in Fort Lauderdale, and Nguyen Ru, an entomologist at the Florida Department of Agriculture and Consumer Services Division of Plant Industry in Gainesville.

Howard is studying the biology of the scale insect and developing chemical controls for it; Pemberton found several kinds of tiny non-stinging wasps during explorations in Asia and is testing them as biological control agents.

Sibyle Schoer, a post-doctoral fellow from Germany, is working with Howard and Pemberton to clarify the relationships between the wasps and the scale insects, while Nguyen is developing mass-rearing techniques for the biocontrol agents.

“Since lobate lac scale is a relatively new pest, there is an urgent need for ways to control it,” Howard said. “Certain insecticides are effective on ornamental plants, but they are not approved for use on fruit trees.”

He said biological control offers the best long-term solution to the scale problem, but the host range of the beneficial predators must be determined to make sure they will attack nothing but the lobate lac scale.

Residents who want to treat lobate lac scale should contract their local UF county extension service office for advice, Howard said.